The present invention relates to a method for identifying a control path of a controlled system, and more particularly to a method for identifying a control path in the presence of deterministic perturbations.
A high-quality identification of a controlled system form an important basis for optimizing a closed-loop control circuit. A controlled system is typically identified by applying a suitable stimulus signal at the input of the controlled system and measuring the path response at the output of the controlled system. The controlled system can be described by a transfer function which can be identified by measuring the path response to the stimulus signal.
The transfer function can be determined either in the time domain by observing the time evolution of the stimulus signal and the path response or, as is commonly done in this technical field, in the frequency domain.
For identifying the controlled system in the frequency domain, both the stimulus signal and the path response are transformed into the frequency domain through a Fourier transform. The transfer function of the controlled system in the frequency domain is obtained in the form of a complex transfer function by dividing the Fourier-transformed path response by the Fourier-transformed stimulus signal.
The frequency response of the magnitude and/or the phase of the complex transfer function of the controlled system can then be determined from the complex transfer function of the controlled system.
In practical applications, perturbations and/or perturbation signals make often make it difficult to reliably identify a path of the controlled system that is to be controlled. A distinction can be made between two types of perturbations that can occur, which can be referred to as stochastic perturbations and deterministic perturbations.
The impact of stochastic perturbation signals on the identification of the controlled system can be lessened by performing a sufficiently large number of averages and/or by low-pass filtering and/or by analyzing the correlation of one or several perturbation signals. However, these measures operate only in a limited fashion with deterministic perturbation signals, or do not work at all.
Errors in the identification of controlled systems in the presence of deterministic perturbation signals have so far been unavoidable and had to be tolerated, since the above-mentioned methods were inadequate to significantly reduce these errors. As a result, the controlled system could not be reliably identified in the frequency range where the deterministic perturbation signals occur.
The European patent publication EP 0 211 374 A1 describes a device for compensating the effect of gravity on an element of a machine-tool or a robot that can be raised and lowered by an electric motor, and a method for operating such a device. The patent application describes optimizing a controller setting by applying a perturbation signal.
It would therefore be desirable and advantageous to provide an easy-to-use and cost-effective method for identifying a control path of a controlled system, which obviates prior art shortcomings and is able to specifically identify a control path in the presence of deterministic perturbations.